JSON for Modern C++ 3.10.4

◆ operator[]() [7/8]

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer, class BinaryType = std::vector<std::uint8_t>>
template<typename T >
reference nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::operator[] ( T *  key)
inline

Returns a reference to the element at with specified key key.

Note
If key is not found in the object, then it is silently added to the object and filled with a null value to make key a valid reference. In case the value was null before, it is converted to an object.
Parameters
[in]keykey of the element to access
Returns
reference to the element at key key
Exceptions
type_error.305if the JSON value is not an object or null; in that cases, using the [] operator with a key makes no sense.
Complexity
Logarithmic in the size of the container.
Example
The example below shows how object elements can be read and written using the [] operator.
1#include <iostream>
2#include <iomanip>
3#include <nlohmann/json.hpp>
4
5using json = nlohmann::json;
6
7int main()
8{
9 // create a JSON object
10 json object =
11 {
12 {"one", 1}, {"two", 2}, {"three", 2.9}
13 };
14
15 // output element with key "two"
16 std::cout << object["two"] << "\n\n";
17
18 // change element with key "three"
19 object["three"] = 3;
20
21 // output changed array
22 std::cout << std::setw(4) << object << "\n\n";
23
24 // mention nonexisting key
25 object["four"];
26
27 // write to nonexisting key
28 object["five"]["really"]["nested"] = true;
29
30 // output changed object
31 std::cout << std::setw(4) << object << '\n';
32}
basic_json<> json
default JSON class
Definition: json.hpp:3472

Output (play with this example online):
2

{
    "one": 1,
    "three": 3,
    "two": 2
}

{
    "five": {
        "really": {
            "nested": true
        }
    },
    "four": null,
    "one": 1,
    "three": 3,
    "two": 2
}
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/operatorarray__key_type.cpp -o operatorarray__key_type 
See also
see at(const typename object_t::key_type&) for access by reference with range checking
see value() for access by value with a default value
Since
version 1.1.0

Definition at line 21383 of file json.hpp.